Abstract

McArdle's disease causes limitation in exercise capacity as well as disability, the severity of which has been associated with the angiotensin-converting enzyme (ACE) insertion (I)/deletion (D) haplotype-patients with the genotype associated with higher ACE activity show the most severe phenotype. Modulation of ACE activity through the use of inhibitors may thus positively affect disease expression. In a double-blind, randomized, placebo-controlled trial, we assessed the efficacy of an ACE inhibitor (2.5 mg ramipril) in 8 patients with McArdle's disease. End-points were changes in parameters of exercise physiology (cycloergometer and muscle 31P-magnetic resonance spectroscopy), quality of life (QoL) according to the Short Form 36 (SF-36), and disability according to the World Health Organization-Disability Assessment Scale II (WHO-DAS II). Patients had lower QoL and higher disability than controls. Measures of exercise physiology were not changed by ramipril in the whole group, but treatment induced higher peak VO2 (P = 0.017) in ACE D/D patients, yet not in I/D patients. Treatment significantly improved disability (P < 0.05). McArdle's disease is a disabling condition affecting patients' QoL. Treatment with ramipril improves disability and modifies exercise physiology only in D/D patients, raising the possibility of a differential haplotype-linked sensitivity to the treatment.